1. Field of the Invention
The present invention relates to methods and apparatus for detecting leaks in particle filtration apparatus, and especially to methods and apparatus for remote sensing of leaks in filter bags, cartridges, or other filter devices in filter houses. A remote leak detection sensing method represents an optimization of the filtration process.
2. Description of Related Art
A common problem in the maintenance of filter houses is the monitoring of filter devices (e.g., filter bags or filter cartridges) for leaks. While leaks from a single filter device (e.g., a cartridge or bag) is not generally difficult to detect, detecting and pin-pointing a leak in a large filter house, having a vast array of filter devices arranged in a matrix of rows and columns is often a very burdensome (and sometimes dangerous) task. As is explained below, none of the current methods for detecting leaks is considered entirely satisfactory.
Leak detection of single bags is currently performed using the so-called "black light" test. In this method, a fluorescent dust is introduced into the raw gas stream upstream the filter house. A compartment in which a leak is suspected has to be taken off-line or shut down, in many cases requiring cooling for several hours so that humans can enter. Usually a maintenance worker wearing protective clothing will then enter the compartment and shine an ultraviolet ("black") light into the clean gas side of the suspect filter devices to search for the fluorescent dust which has leaked into the clean gas side. Leaks are detected in those filter devices containing fluorescent dust on their clean side. The same method is used to detect leaks in the installation area of bags in the tube sheet. Needless to say, this is an expensive and time consuming process. When the leaking filter device is not found in the suspected compartment, another compartment must then be shut down, with resulting interruption of normal operation and with a resulting release of hazardous filtrates into ambient air. Also, it is a dangerous job to climb into a filter house--high temperatures, poisonous gases, and poisonous dusts (e.g., dusts containing dioxins and furans as well as heavy metal) are found frequently in this environment. Although the black light test is the most commonly used method to detect leaks, it can only be used when excessive dust concentrations in the flue gas are observed using a different method such as continuous emission monitoring systems (e.g., CEMS, opacity meters).
Opacity test methods are used to detect dust emissions in the flue gas exiting the gas cleaning equipment through the stack. The opacity test measures light extinction of a light ray through dust particulates dispensed in the gas stream as it exits a flue gas stack. These measurements are conducted only in the stack to quantitatively determine a dust leak, not to specifically locate broken or badly installed filter bags. Commercial opacity meters include those available from Bailey Controls Co., Wickliffe, Ohio, Datatest, Inc., Levittown, Pa., Enviroplan, Inc., Indianapolis, Ind., Land Combustion, Inc., Bristol, Pa., Monitor Labs Corp., Englewood, Colo., Montrol Co., Farmington Hills, Mich., and others.
Remote sensing of dust particle concentrations have been studied in other application areas. See, e.g., G. Ramachandran et al., "Extraction of Aerosol-Size Distributions from Multispectral Light Extinction Data," 17 Aerosol Science and Tech. 303-25 (1992); G. Ramachandran et al., "Extraction of Aerosol-Size Distributions from Multispectral Light Extinction Measurements with Computed Tomography," 11 J. Opt. Soc. Am. A 144 (January 1994); Todd et al. "Evaluation of Algorithms for Tomographic Reconstruction of Chemical Concentrations in Indoor Air," 55 Am. Ind. Hyg. Assoc. J. 403 (May 1994). The object of this research was to detect the dust concentration, dust particle size distribution, and gas composition in indoor air (e.g., workplace air exposed to workers in industry). Their idea was a real-time measurement of ambient air composition. This goal was to be achieved by using a few lasers scanning the room air in a two dimensional plane. To reduce the number of lasers and detectors needed to scan a wide area, it was proposed that a series of mirrors could be installed to reflect the light beams through extended paths between each laser and its respected detector or detectors. These investigations resulted in theoretical solutions for remote sensing of workplace contamination, but, apparently, no practical embodiment of such a system has been developed.
Until the present invention, it has not been proposed to try and adapt these kinds of remote sensing systems for use in monitoring the status of filter devices in a filter house. Perhaps one reason for this is that filter houses require special installation parameters due to the extreme harshness of that environment. For example, a typical filter house is replete with vibrations, acidic gases, high temperatures, and "upset" conditions in which the dust concentrations, even on the clean gas side of a filter, can be substantial.
Accordingly, it is a primary purpose of the present invention to provide reliable and efficient method and apparatus for detecting changes in status of filter devices in a filter house.
It is a further purpose of the present invention to provide a method and apparatus for detecting changes in status of filter devices in a filter house that allow leaking devices to be rapidly identified with minimal disruption in the operation of the filter house and with reduced environmental impact.
It is still another purpose of the present invention to provide a method and apparatus for detecting changes in the status of filter devices in a filter house that allow monitoring of particle size and concentration.
These and other purposes of the present invention will become evident from review of the following specification.